1. Field of the Invention
This invention relates to a steering device for a vehicle for use in turning front wheels together with rear wheels in response to a steering operation of the steering wheel.
2. Description of the Relevant Art
In Japanese patent application Nos. 56-118698 and 57-47743, there is disclosed a steering device for a vehicle which provides a simultaneous turning of the front and rear wheels by a method wherein a rotation required for turning rear wheels is produced as a turning of an oscillating linkage and an eccentric pin, etc., from a front wheel turning system, through a linkage member.
The above-mentioned steering device enables the rear wheels to be turned in the same direction as that of the front wheels under an operation of the steering wheel in a small steering angle and also turned in an opposite direction with a large steering angle operation, with the result that an operating characteristic during high speed travel of the vehicle is improved and manueverability of the vehicle is improved due to the fact that a small radius of curvature can be obtained with a large steering angle when effecting a U-turn operation or when entering or exiting of the vehicle to and from a parking place, etc.
However, turning of the rear wheels in such device is performed through a pivotal movement of the oscillating linkage or eccentric pin etc., such that a turning angle of the rear wheels is dependent upon a relatively simple function.
That is, in the above-mentioned steering device, the turning angle of the rear wheels with respect to the steering angle of the steering wheel is given as a sine function, with the result that one maximum turning angle of the rear wheels when steered in the same direction as that of the front wheels and the other maximum turning angle of the rear wheels when steered in a direction opposite to that of the front wheels, are equal to each other.
Therefore, there has been a tendency that factors such as the most frequently occurring ranges of travel speed during normal use of the vehicle were not taken into consideration when the above-described steering device was applied to various kinds of vehicle.
For example, in a vehicle which is operated in only a low speed range, it seems preferable to have one maximum turning angle of the rear wheels in the same direction as that of the front wheels smaller than the other maximum turning angle of the rear wheels in a direction opposite to that of the front wheels, rather than to have an equal setting of the two maximum turning angles of the rear wheels as described above, so as to provide the aforesaid improvements.
It will be understood that a setting of a characteristic of variation in the turning angle of the rear wheels with respect to a variation of the steering angle of the steering wheel based on use of the vehicle can further dramatically improve operation of a vehicle provided with the above-mentioned conventional vehicle steering device per se.
The present invention provides a further improvement of the above-described conventional type of vehicle steering device.